1. Field of the Invention
The present invention relates to a far-infrared radiating system employing a far-infrared radiating element which radiates far-infrared rays upon heating.
2. Description of the Prior Art
Hitherto, in a conventional type of such far-infrared radiating system, a heat source thereof is provided by an electric heater or a combustion gas produced in a burner or a catalyst unit.
The heat source employing the electric heater is disadvantageous in its operation cost. On the other hand, the heat source employing the combustion gas suffers from a problem that, since a temperature of the combustion gas is generally too high in use, a temperature of a far-infrared radiating element becomes too high to cause energy densities of far-infrared rays to become high, i.e., to cause wavelengths of the far-infrared rays to become short.
When an organic material which has an upper limit of allowable temperature is irradiated with the far-infrared rays having short wavelengths or high energy densities in order to dry the organic material, a temperature of a peripheral portion of the thus irradiated organic material is exclusively increased to produce a considerable difference in temperature between the peripheral portion of the organic material and an interior portion of the same.
In this case, in order to eliminate such difference in temperature of the irradiated organic material, it is necessary to employ far-infrared rays having long wavelengths or low energy densities in heating of the organic material, which heating is conducted for a relatively long period of time by the use of the far-infrared radiating element which is kept relatively low in temperature while provided with a relatively large radiating area.
However, in order to keep the far-infrared radiating element low in temperature, it is necessary to feed a large amount of a secondary combusting gas to the large radiating area of the far-infrared radiating element, which secondary combustion gas is prepared by mixing a primary combustion gas with a large amount of air so as to decrease a temperature of the secondary combustion gas. Consequently, in this case, there is a defect in that such large amount of the secondary combustion gas has a high consumption of power in its feeding operation.
On the other hand, in case that a multistage catalytic-combustion process is employed in order to increase a thermal efficiency of the far-infrared radiating system, there is another defect in that a large amount of a catalyst must be employed in such multistage catalytic-combustion process to ensure a low-temperature combustion operation, which leads to a large amount of pressure loss of a combustion gas which is produced in such low-temperature combustion operation and is forced to pass through a layer of the large amount of the catalyst with a high consumption of power.